1. Field of the Invention
The invention relates in general to elevator systems, and more specifically to elevator systems having a plurality of cars controlled by a system processor.
2. Description of the Prior Art
Elevator systems of the prior art which have a plurality of cars controlled by a central dispatcher control system, commonly operate in one of a plurality of different modes, with the specific mode selected at any one time depending upon traffic conditions. The "events" which are detected by the control system to sense which mode the system should be operating in are generated by hardware, the decision making control for determining the operating strategy or mode is hardwired, and the system input signals are received and processed in parallel to generate parallel output signals for control of the various elevator cars.
A programmable dispatcher, including a digital computer and a software package for directing the computer hardware to the specific task of elevator car dispatching, would have many advantages over the conventional hardwired dispatcher control system. For example, with the decision making and operating mode strategy confined to the software package, the hardware car controller and car station for the individual cars may be substantially identical for each elevator installation. The specific strategy employed for each installation would be tailored according to its requirements, and later changed, if desired, without modification of the hardware. For example, changes in the usage of a particular building which require a different strategy for the associated elevator system than that originally employed, may be easily changed when the strategy is in the form of software, by making the desired changes in the software program and storing the new program in the memory of the computer.
The change from a hardwired dispatcher to a programmable one, however, is not as straightforward as might be expected. Hardwired dispatchers have many logic elements, enabling them to process signals in parallel. With a digital computer, the number of logic elements is severely restricted, necessitating sequential processing of signals. Each input signal must, therefore, be observed in turn, and each output signal generated in turn. To remove the need for precise timing of input and output signals, which would complicate the program and create difficulties in synchronizing the transmission of the signals, it is advantageous to employ storage devices at the interface or buffer between the programmable processor or digital computer and the hardwired control of the elevator system.
The software of a programmable dispatcher must perform such basic functions as the reading and storing of car status data, for each elevator car in the system, reading and storing corridor call data, processing the stored system data to determine the most advantageous pattern of call allocation and service assignments to the elevator cars, sending commands to stationary cars to initiate the cars on a predetermined service assignment, sending stop requests to moving elevator cars to stop them at selected floors, and outputting signals indicative of system conditions for the proper functioning of other system components.
The program for performing these functions may require a substantial amount of running time, especially when the elevator system is experiencing peak loads. For example, if the running time of the program is such that the time between receiving the car status data and the outputting of a stop request to a moving car based on this data, is long enough for the moving car to have moved past the deceleration point for the floor at which the car was to stop, the stop request would be "stale" and the call for this floor would have to be reallocated on the next run through the program.
Therefore, it would be desirable to provide a new and improved elevator system which includes a programmable dispatcher, with the programmable dispatcher operating in such a manner that it efficiently performs all of its necessary functions while providing valid stop signals from moving cars.